Very possible. Instead of only the value argument of the setFilter statement being a variable, both the field and the value would be a variable. Something like this:
let searchValue = $w("#searchBar").value;
let fieldName = $w("#fieldDropdown").value;
$w('#dataset1').setFilter(wixData.filter()
.eq(fieldName, searchValue)
)
.then(() => {
console.log("filter set");
})